This invention relates to the art of gas burning torches for welding, cutting and the like and, more particularly, to an improved valve for controlling the flow of a gas in such a torch.
It is of course well known to provide a gas burning torch for welding, cutting or the like with a flow control or throttling valve which is manually adjustable to control the flow of preheat oxygen in a cutting torch or cutting attachment, or to control the flow of oxygen for mixture with a fuel gas such as acetylene to provide a combustible mixture in connection with use of the torch for welding. Heretofore, as shown in U.S. Pat. No. 3,255,803 to Hach et al, for example, such manually operable flow control valves have included a rotatable valve stem which is threadably interengaged with a threaded bore provided therefor in a valve housing. The outer end of the stem is axially splined to receive an operating knob by which the stem is rotated and an adjustable packing is provided about the stem between the housing and a bonnet member threatedly mounted on the housing. Rotation of the valve stem displaces the valve element end thereof into and out of engagement with a seat in a flow passageway through the housing to respectively close and open the passageway to the flow of gas therethrough. A spring is interposed between the operating knob and bonnet to load the threads between the stem and housing. It is not uncommon, however, to rely solely on the adjustable packing in such valves to obtain valve stability with respect to gas flow rate therethrough.
Gas flow control valves of the foregoing character have a number of disadvantages including misalignment between the valve element portion of the stem and the valve seat occurring as a result of bending of the stem, wear and/or manufacturing errors and which misalignment leads to the need for excessive torquing in an effort to achieve adequate sealing engagement between the seat and valve element portion of the stem when the valve is closed. Further, the need for such excessive torquing itself promotes wear of the valve element portion of the stem and/or the seat which shortens the otherwise useful life of the valve. Still further, the rotatable nature of the valve stem by threaded interengagement with the valve body promotes wear of the threads, and this too can affect alignment of the stem and seat as well as the useful life of the valve. Such rotation of the stem also causes wear of the packing, and the latter must be adjusted periodically in order to maintain stability against thread backlash which can cause changes in gas flow rate due to inadvertent external forces on the operating knob. The latter is a problem even if the stem is loaded as in the patent to Hach et al in that the packing provides a portion of the torque control of the stem against backlash. In connection with such wear and/or concentricity problems, it will be appreciated that these problems cannot be adequately overcome simply by replacing the valve stem portion of the valve assembly in that such wear affects the threads in the housing and the valve seat in the flow passageway therethrough. Accordingly, replacement of the entire valve assembly is most often required. In addition to the foregoing problems, the direct connection between the operating knob and valve stem is subject to breakage and subjects the valve stem to bending under normal abuse during use. Such abuse, whether causing bending of the stem or not, can cause the misalignment problems referred to above, or further promote such misalignment and thus the wear problems resulting therefrom.